Lidocaine is used for the purpose of local anesthesia or topical anesthesia. The usage form of lidocaine is an external preparation comprising lidocaine or a patch comprising lidocaine. Examples of external preparations include ointment, cream, jelly, spray, etc., which are used, for example, for topical anesthesia of the skin in the treatment of postherpetic neuralgia. Examples of patches include aqueous base patches (cataplasms) and non-aqueous patches (tapes).
An example of aqueous base patches is Lidoderm (registered trademark of Endo Pharmaceuticals (U.S.)), which is mainly used for topical anesthesia of the skin in the treatment of postherpetic neuralgia, and is also used to relieve pain in various muscles. Aqueous base patches have thick plasters because they contain moisture; therefore, aqueous base patches are poorly compatible with the skin. Moreover, due to very little adhesion, aqueous base patches are difficult to be attached to the skin for a long period of time. Furthermore, the vaporization of moisture problematically causes changes in adhesion and physical properties. Additionally, in order to make lidocaine permeate into the muscle, it is necessary to dissolve lidocaine, and moisture is thus required to dissolve lidocaine.
Next, as a non-aqueous patch, for example, patent Japanese Patent No. 3159688 (patent Document 1) discloses a technique for alleviating postherpetic neuralgia, in which 5 to 30 wt. % of lidocaine is added as a local anesthetic. Japanese Unexamined Patent Publication No. 7-215850 (Patent Document 2) discloses a technique relating to a percutaneous absorption tape for local anesthesia comprising 5 to 100 wt. % of lidocaine. Japanese Unexamined Patent Publication No. 9-315964 (Patent Document 3) and Japanese Unexamined Patent Publication No. 2001-392501 (Patent Document 4) disclose techniques relating to a patch comprising 0.5 to 5 mass % of lidocaine. WO 2009/060629 (Patent Document 5) discloses a technique relating to a patch comprising 10 to 40 mass % of lidocaine. These non-aqueous patches have poor permeability to the skin because the lidocaine is not dissolved and is present in a crystalline state.
In addition, the technique disclosed in Patent Document 5 uses a high concentration of lidocaine. It is pointed out that lidocaine has an adverse effect on the heart. Prolonged use of a high concentration of lidocaine causes side effects, such as shock, rubor, and irritating sensation. External preparations comprising more than 5 mass % of lidocaine are designated as powerful drugs, and cannot be used as household (nonprescription) medicine.
In contrast, the techniques disclosed in Patent Documents 3 and 4 use a small amount of lidocaine, and can be used for household use; however, even after the small amount of lidocaine is completely dissolved, the lidocaine cannot be stably released over a long period of time (e.g., 12 hours or more) and cannot permeate into the skin. Thus, there is a problem with the pain-relieving effect.